OTTAWA, March 8 (Reuters) - The Liberals would return to power in the next Canadian election if, as expected, they choose the son of former Prime Minister Pierre Trudeau to head the party, according to an opinion poll released on Friday.

The Forum Research poll showed the Liberals with Justin Trudeau as leader would be able to replace the Conservatives in power, albeit with a minority government, if an election were held today.

The center-left Liberals governed Canada for much of the 20th century, but fell to third place in the 2011 election. That left them behind the left-leaning New Democrats for the first time in history as the Conservatives turned their previous minority government into a majority one.

The Forum poll showed the Liberals under Trudeau would take 39 percent of the vote if an election were held now, compared with 32 percent for the Conservatives, and 20 percent for the New Democrats.

An election is not due until 2015, and the Conservatives have not yet ground Trudeau through their formidable advertising machine, making it impossible to predict if the poll figures will hold.

"Justin Trudeau continues to solidify his position at the top of the pops," the National Post newspaper, which ran the poll, quoted Forum President Lorne Bozinoff as saying.

Trudeau is a magnetic 41-year-old former teacher and ski instructor who has attracted 150,000 supporters to the Liberal Party during his leadership campaign, more than all the other leadership candidates combined. He heads into the April 14 convention as the heavy favorite.

His flamboyant father held power from 1968 to 1979 and again from 1980 to 1984. He died in 2000.

Justin Trudeau's popular support comes despite widespread doubts in Ottawa on whether he has the clout to become prime minister. He has given few specifics on how he would run Canada other than offering generic goals such as protecting and expanding the middle class.

The Conservatives will be sure to seize on some of his gaffes, such as saying he might consider joining Quebec separatists if Canada became too conservative.

'UNCRITICAL COVERAGE'

Conservative Party Citizenship and Immigration Minister Jason Kenney said Trudeau had received "largely uncritical coverage" so far in the race, and that polls were irrelevant this far ahead of the election.

"Sooner or later if he becomes Liberal leader, he'll have to undergo a greater degree of public scrutiny, and that goes with the job," he told Reuters after a speech in Ottawa.

Forum said its latest poll numbers would give a Trudeau-led Liberal Party 149 seats in the House of Commons, compared with 115 for the Conservatives and 41 for the New Democrats.

A party needs 155 of the 308 seats in the House to get a majority that cannot be overturned by other parties, although the formula will change when more seats are added for the next election.

The poll showed support for the Liberals at 30 percent in response to questions that did not mention Trudeau, just behind the Conservatives at 31 percent, and ahead of the New Democrats at 27 percent.

A Nanos poll released on Thursday showed the Conservatives at 31.5 percent of committed voters, their lowest Nanos result since August 2009. Nanos has the Liberals at 29.1 percent and the New Democrats at 27.2 percent.

The automated Forum telephone poll surveyed 1,755 Canadians on Wednesday and Thursday. Forum says it has a margin of error of 2 percentage points, 19 times out of 20.